The flower or ornamental plant industry strives to develop new and different varieties of flowers and/or plants. An effective way to create such novel varieties is through the manipulation of flower color. Classical breeding techniques have been used with some success to produce a wide range of colors for almost all of the commercial varieties of flowers and/or plants available today. This approach has been limited, however, by the constraints of a particular species' gene pool and for this reason it is rare for a single species to have the full spectrum of colored varieties. For example, the development of novel colored varieties of plants or plant parts such as flowers, foliage and stems would offer a significant opportunity in both the cut flower and ornamental markets. In the flower or ornamental plant industry, the development of desired (including novel) colored varieties of carnation is of particular interest. This includes not only different colored flowers but also anthers and styles.
Flower color is predominantly due to three types of pigment: flavonoids, carotenoids and betalains. Of the three, the flavonoids are the most common and contribute a range of colors from yellow to red to blue. The flavonoid molecules that make the major contribution to flower color are the anthocyanins, which are glycosylated derivatives of cyanidin and its methylated derivative peonidin, delphinidin and its methylated derivatives petunidin and malvidin and pelargonidin. Anthocyanins are localized in the vacuole of the epidermal cells of petals or the vacuole of the sub epidermal cells of leaves.
The flavonoid pigments are secondary metabolites of the phenylpropanoid pathway. The biosynthetic pathway for the flavonoid pigments (flavonoid pathway) is well established, (Holton and Cornish, Plant Cell 7:1071-1083, 1995; Mol et al, Trends Plant Sci. 3:212-217, 1998; Winkel-Shirley, Plant Physiol. 126:485-493, 2001a; and Winkel-Shirley, Plant Physiol. 127:1399-1404, 2001b, Tanaka and Mason, In Plant Genetic Engineering, Singh and Jaiwal (eds) SciTech Publishing Llc., USA, 1: 361-385, 2003, Tanaka et al, Plant Cell, Tissue and Organ Culture 80: 1-24, 2005, Tanaka and Brugliera, In Flowering and Its Manipulation, Annual Plant Reviews Ainsworth (ed), Blackwell Publishing, UK, 20: 201-239, 2006). Three reactions and enzymes are involved in the conversion of phenylalanine to p-coumaroyl-CoA, one of the first key substrates in the flavonoid pathway. The enzymes are phenylalanine ammonia-lyase (PAL), cinnamate 4-hydroxylase (C4H) and 4-coumarate: CoA ligase (4CL). The first committed step in the pathway involves the condensation of three molecules of malonyl-CoA (provided by the action of acetyl CoA carboxylase (ACC) on acetyl CoA and CO2) with one molecule of p-coumaroyl-CoA. This reaction is catalyzed by the enzyme chalcone synthase (CHS). The product of this reaction, 2′,4,4′,6′, tetrahydroxy-chalcone, is normally rapidly isomerized by the enzyme chalcone flavanone isomerase (CHI) to produce naringenin. Naringenin is subsequently hydroxylated at the 3 position of the central ring by flavanone 3-hydroxylase (F3H) to produce dihydrokaempferol (DHK).
The pattern of hydroxylation of the B-ring of DHK plays a key role in determining petal color. The B-ring can be hydroxylated at either the 3′, or both the 3′ and 5′ positions, to produce dihydroquercetin (DHQ) or dihydromyricetin (DHM), respectively. Two key enzymes involved in this part of the pathway are flavonoid 3′-hydroxylase (F3′H) and flavonoid 3′, 5′-hydroxylase (F3′5′H), both members of the cytochrome P450 class of enzymes.
The production of colored anthocyanins from the dihydroflavonols (DHK, DHQ, DHM), involves dihydroflavonol-4-reductase (DFR) leading to the production of the leucoanthocyanidins. The leucoanthocyanidins are subsequently converted to the anthocyanidins, pelargonidin, cyaniding, and delphinidin. These flavonoid molecules are unstable under normal physiological conditions and glycosylation at the 3-position, through the action of glycosyltransferases, stabilizes the anthocyanidin molecule thus allowing accumulation of the anthocyanins.
Nucleotide sequences encoding F3′5′Hs have been cloned (see International Patent Application No. PCT/AU92/00334, incorporated herein by reference, Holton et al, Nature, 366:276-279, 1993, and International Patent Application No. PCT/AU03/01111, incorporated herein by reference). These sequences were efficient in modulating 3′, 5′ hydroxylation of flavonoids in petunia (see International Patent Application No. PCT/AU92/00334 and Holton et al, 1993 supra), tobacco (see International Patent Application No. PCT/AU92/00334), carnations (see International Patent Application No. PCT/AU96/00296, incorporated herein by reference), and roses (see International Patent Application No. PCT/AU03/01111).
Cytochrome b5 proteins(Cyt b5) are common to animals, plants and yeast (De Vetten et. al., 1999). Experiments show that Cyt b5 can accept electrons from either NADH-cytochrome reductase or NADPH-Cyt P450 reductase and donate electrons to different desaturases involved in lipid biosynthesis and/or to members of the Cyt P450 superfamily. In 1999, De Vetten et. al. demonstrated that Cyt b5 was required for the full activity of petunia F3′5′H in vivo and therefore for the generation of purple/blue flower colors in petunia.
Carnations are one of the most extensively grown cut flowers in the world.
There are thousands of current and past cut-flower varieties of cultivated carnation. These are divided into three general groups based on plant form, flower size, and flower type. The three flower types are standards, sprays, and midis. Most of the carnations sold fall into two main groups, the standards and the sprays. Standard carnations are intended for cultivation under conditions in which a single large flower is required per stem. Side shoots and buds are removed (a process called disbudding) to increase the size of the terminal flower. Sprays and/or miniatures are intended for cultivation to give a large number of smaller flowers per stem. Only the central flower is removed, allowing the laterals to form a ‘fan’ of flowers.
Spray carnation varieties are popular in the floral trade, as the multiple flower buds on a single stem are well suited to various types of flower arrangements and provide bulk to bouquets used in the mass market segment of the industry.
Standard and spray cultivars dominate the carnation cut-flower industry, with approximately equal numbers sold of each type in the USA. In Japan, Spray-type varieties account for 70% of carnation flowers sold by volume, whilst in Europe spray-type carnations account for approximately 50% of carnation flowers traded through out the Dutch auctions. The Dutch auction trade is a good indication of consumption across Europe.
While standard and midi-type carnations have been successfully manipulated genetically to introduce new colors (Tanaka and Brugliera, 2006, supra; see International Patent Application No. PCT/AU96/00296), this has not been applied to spray carnations. There is an absence of blue color in color-assortment in carnation, only recently filled through the introduction of genetically-modified standard-type carnation varieties. However, standard-type varieties cannot be used for certain purposes, such as bouquets and flower arrangements where a large number of smaller carnation flowers are needed, such as hand-held arrangements and small table settings.
One particular spray carnation which is particularly commercially popular is the Cerise Westpearl line of carnations (Dianthus caryophyllus cv. Cerise Westpearl). The variety has excellent growing characteristics and a moderate to good resistance to fungal pathogens such as Fusarium. 